The present invention relates in general to fluorescent lamps used to illuminate a display, and more particularly to a fluorescent lamp providing more uniform illumination to backlight a display.
Tubular fluorescent lamps are often used to back light or illuminate a display, such as a liquid crystal display. The fluorescent lamps are usually bent or curved forming a serpentine shape with rounded bends. The bends or curves in the tubular fluorescent lamps have a radius curve. These curves often prevent an adjacent display from being uniformly illuminated. As a result, often portions of the display appear darker than other portions of the display. These dark regions are often in corners of a quadrilateral, rectangular, or square display. These dark regions are undesirable and often lead to the display being less legible or difficult to read.
Additionally, there are dark spaces associated with gas discharge lamps, such as fluorescent lamps. There are several dark spaces adjacent the cathode of a gas discharge lamp. One of these spaces is the Aston dark space. This dark space is a space of unexcited atoms which occurs because the electrons leaving the electrode have less energy than that necessary to produce excitation of the atoms or molecules with which they collide. There are additional dark spaces a predetermined distance from the cathode, such as the Crookes dark space and the Faraday dark space. The Faraday dark space is typically furthest from the electrode. After the Faraday dark space a positive column is formed generating substantially uniform brightness over the remaining length of the tubular gas discharge lamp. The anode also has a dark space associated therewith. Accordingly, the illumination intensity or brightness along the length of a fluorescent tube gas discharge lamp is not uniform. This non-uniformity of illumination or brightens, when used to back light a display, causes difficulty in reading the display and interpreting information contained thereon. This is particularly disadvantageous in critical applications, such as those used in instrumentation, for example in avionics. In avionics, it is critical for features displayed to have a visibility as intended over the entire surface and not to be affected by dark regions of the back light illumination. Improperly backlighting the display or providing a back light that is not uniform in intensity may cause such hazardous results as a misreading of the display. Accordingly, it is essential that in backlighting of displays, especially in avionics or critical applications, that the backlighting illumination intensity be as uniform as possible over the entire planar surface of the display. The displays are often quadrilateral or rectangular, making it difficult to uniformly illuminate the corners of the quadrilateral or rectangular display using existing curved serpentine type gas discharge fluorescent tubes.
The present invention provides a fluorescent lamp having substantially improved uniform brightness or intensity along the length of the lamp. One embodiment of the present invention has an angled leg having an electrode placed therein. The electrode is spaced a predetermined distance from a central portion of the tubular envelope of the fluorescent lamp so as to be beyond the dark spaces in the gas discharge of the fluorescent lamp.
In another embodiment of the present invention, right angled bends are formed in the fluorescent lamp so as to more uniformly illuminate a square or rectangular display eliminating dark regions over portions of the display.
Another embodiment of the present invention is a method of making right angled bend in a tubular fluorescent lamp.
Accordingly, it is an object of the present invention to provide a fluorescent lamp capable of providing a substantially uniform back light illumination for a display.
It is an advantage of the present invention that dark regions over portions of a display are prevented.
It is a further advantage of the present invention that a display may more easily be read and information thereon displayed more accurately.
It is a feature of the present invention that the electrode in a gas discharge fluorescent lamp is spaced within a right angled bend of a leg of the gas discharge fluorescent lamp a predetermined distance so as to be beyond any dark spaces in the discharge of the lamp.
These and other objects, advantages and features will become readily apparent in view of the following more detailed description.